As is well-known, radiating coaxial cables present a special problem in meeting fire safety tests because of the numerous holes that must be provided in the outer conductor of a radiating cable. In addition to allowing the cable to radiate, these holes allow the molten polymer insulation to flow out of the cable, in the event of a fire.
The most stringent fire safety test to be met by radiating cables is the test required for plenum applications, which is the Flame Test described in Standard UL 910, also known as the "Steiner Tunnel" test for plenum cables. The only radiating coaxial cables which are known to pass the above test are those which use a fluoropolymer for both the external jacket and a foam dielectric between the inner and outer conductors. Fluoropolymers have an inherently high level of flame resistance. However, fluoropolymers present other problems because they generate large amounts of toxic fumes and corrosive gases when burned.